1. Field of the Invention
This invention relates to devices used for the reinforcement of a door frame. The reinforcement disclosed in the present invention cooperates with a door latch strike plate to render the door frame resistant to being kicked or otherwise forcibly opened.
2. Description of Related Technology
Many configurations of door locks and bolt keeper strike plates have been proposed for providing sturdier and tighter fitting door arrangements. For example, U.S. Pat. No. 3,767,245, issued to Keefe, shows an arrangement in which a strike plate is enlarged and extended to lie between the door frame side rail and the door stop. The enlargement receives additional fastening screws. The door jamb is routed out to form a recess for receiving the strike and anchor plate with the striking surface of the keeper strike plate being flush with the surface of the door jamb. A door stop stripping is mounted on the door jamb over the elongated anchor plate. This device is not applicable to all doors because many door jambs are molded, and thus do not lend themselves to the routing operation required for mounting the plate. Also, the stripping, or trim, can be pried away leaving the anchoring screws exposed.
U.S. Pat. No. 3,815,945, issued to Lamphere, discloses a door frame security plate designed to prevent the door from being kicked in. The Lamphere device uses a specially milled side rail interlock with an enlarged, configured and extended strike plate perforated to receive more than the customary number of fastening screws. The screws are long enough to penetrate into the wood construction immediately abutting the door casing side rail. This apparatus, however, requires additional weakening of the jamb by milling out a seat for the security plate and, in addition, the plate extends in the general direction of any force that would be applied to break in. Therefore, it fails to provide a desirable reinforcement securing the frame against being split.
U.S. Pat. No. 3,9l8,207, issued to Aliotta, discloses a plate guard with a striker. The plate runs parallel to the opening on the striker plate and utilizes a lip member which rests at the frame edge. Thus, the Aliotta reference is in fact using an enlarge striker plate.
U.S. Pat. No. 3,967,845, issued to Gobernale, discloses a small metal reinforcing plate that is arranged beneath the usual striker plate in a routed recess of the wooden door jamb. The metal plate has small protrusions which extend into the jamb itself, but the primary resistence to forceful entry is still provided by wood screws that extend through both the original striker plate and the metal reinforcement plate. The Gobernale device reinforces the area immediately surrounding the striker plate, but does not address the larger problem of reinforcing the door jamb itself.
U.S. Pat No. 4,005,890, issued to Murch, provides a striker guard to be inserted along with the bolt receiver or striker plate. The guard itself is a flat metal bar which extends from the striker plate chamber into the door frame. This device when subjected to a kicking force permits the device to tip, that is the reinforcement member reflects, either because the metal making up the guard member bends, or the entire member itself rotates slightly within the door frame. In either case, the lock plunger is permitted to slip by the reinforcement guard member.
U.S. Pat. No. 4,057,275, issued to LaBeaud, discloses an elongated metal plate for fastening to the back of a wooden door jamb. In practice, this unit is suitable only for installation on a new door since it requirs removal of the entire side of the door jamb. Although the plate itself has substantial surface area, the portion of the plate which directly resists the force of the plunger consists of only a small lip formed at the edge of the reinforcement plate.
U.S. Pat. No. 4,074,484, issued to Queren, discloses a plate guard for the striker. In order to combat entry by means of kicking the door or using a crowbar at the point at which the locking means engages the door and the frame, the Queren device relies on a plate means to try and reinforce the door jamb itselt. The plate is inserted along the inside face of the frame at right angles to the striker plate. The holding screws used in the device are aligned in the same direction as the force which would be applied to the door during a forced entry. Thus, the holding screws would tend to be pulled out in a longitudinal direction, thus eliminating the possible use of nails as a fastener and relying entirely on the threads of a wood screw to provide resistance to the locked plunger.
U.S. Pat. No. 4,174,862, issued to Shane, discloses a U-shaped metal plate used for reinforcing a door frame. While this device provides great strength, it can only be installed during the initial construction phase because of its considerable size and interaction with the wall itself. The fixed dimensions of the device do not allow for any shimming or adjustment as would be required if the device would be retrofitted on an existing door. Finally, the shape of the device requires that the plunger extend a considerable distance into the reinforcing plate, thereby requiring the use of a deadbolt lock rather than a conventional door plunger.
U.S. Pat. No. 4,186,954, issued to Detlefs, discloses a lock strike plate assembly having a reinforcement rod that extends to the door frame and wall support. Due to the shape of the strike plate chamber, the strike plate itself is secured by wood screws only to the very edge of the door frame. The reinforcing rod, while extending a considerable distanced into the wall support, offers no resistance to twisting, but only to a shear force, and the shear force is resisted only by the rather small cross-sectional area where the reinforcing rod is welded to the strike plate chamber. In practice, the rod would tend to snap off under the force of a sudden blow and the remainder of the plate would easily deform under the twisting force which could be resisted only by the very small volume of wood gripped by the mounting screws.
U.S. Pat. No. 4,195,870, issued to Percoco, discloses a striker plate assembly secured to the door frame. A number of embodiments are shown. Each of the embodiments suffers from either being mounted too close to the edge of a door frame (FIG. 2), offering little resistance to shear force because the reinforcement mechanisms are only narrow rods (see rod 36 welded to plate 37 in FIG. 3) or the plate assembly is very difficult to install. Several of the embodiments include a great number of alignment holes and the use of abnormally long drills needed to accomplish installation. U.S. Pat. No. 4,211,442, issued to Hansen, discloses a strike plate for receiving a lock plunger. The Hansen device is mounted at the edge of the door frame studding with only a single screw, leaving a small volume of wood to resist any striking force. Because of the single screw mounting arrangement, this device may be easily tipped or rotated on impact.
U.S. Pat. No. 4,369,994, issued to Vorves, discloses a strike plate support utilizing rods extending into the door frame. The strength of this device is entirely dependent on the integrity of hinge pin 18. The use of rods as reinforcing members offers little resistance to rotating or slippage, being better suited for resisting only a pure shear force.
U.S. Pat. No. Re. 31,276, issued to Schlage, discloses a lock strike casing which fits into the door jam. The resistance to a shear force of this device is dependent solely on the strength of the wood screws holding the device into the door frame. When subjected to a striking or kicking force, the screws can be bent or pulled from the door jamb, or the door jam itself may be loosened directly, allowing the casing to twist and fall.
U.S. Pat. No. 4,416,087, issued to Ghatak, discloses a door frame reinforcing plate. Due to the fact that pilot holes must be drilled in order to install screws 28, the only part of this device which offers any resistance to a striking force are nuts 36. Thus, when subjected to a striking or kicking force this device tends to pull from the door frame since the bolts 28 offer no more resistance than nails except for the nuts placed on the ends. This device is also quite complicated to install because of the critical alignment required between the pilot holes, bolts, nuts and screws.
None of these prior art proposals solves the problem of preventing forced entry through a door by means of an easily retrofittable structural member. While some of the devices are quite strong, they entail major structural modifications. The other devices disclosed rely entirely on the door frame or the surface layer of the surrounding structure to provide resistance to forced entry. Although the devices themselves are quite strong in many cases, they merely act as a lever arm in removing the entire door jamb. The best solution to this problem is one which would derive strength from the wall of the structure surrounding the door yet which could be easily placed on an existing door without the need for structural modification, nor special fasteners with critical alignment of parts during installation.